Sequence: smallest number with exactly n divisors: Difference between revisions
Sequence: smallest number with exactly n divisors (view source)
Revision as of 14:08, 12 April 2019
, 5 years agoMove F# from anti-primes plus to here
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(Move F# from anti-primes plus to here) |
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The first 15 terms of the sequence are:
1 2 4 6 16 12 64 24 36 48 1024 60 0 192 144
</pre>
=={{header|F_Sharp|F#}}==
This task uses [http://www.rosettacode.org/wiki/Extensible_prime_generator#The_function Extensible Prime Generator (F#)]
<lang fsharp>
// Find Antı-Primes plus. Nigel Galloway: April 9th., 2019
// Increasing the value 14 will increase the number of anti-primes plus found
let fI=primes|>Seq.take 14|>Seq.map bigint|>List.ofSeq
let N=Seq.reduce(*) fI
let fG g=Seq.unfold(fun ((n,i,e) as z)->Some(z,(n+1,i+1,(e*g)))) (1,2,g)
let fE n i=n|>Seq.collect(fun(n,e,g)->Seq.map(fun(a,c,b)->(a,c*e,g*b)) (i|>Seq.takeWhile(fun(g,_,_)->g<=n))|> Seq.takeWhile(fun(_,_,n)->n<N))
let fL=let mutable g=0 in (fun n->g<-g+1; n=g)
let n=Seq.concat(Seq.scan(fun n g->fE n (fG g)) (seq[(2147483647,1,1I)]) fI)|>List.ofSeq|>List.groupBy(fun(_,n,_)->n)|>List.sortBy(fun(n,_)->n)|>List.takeWhile(fun(n,_)->fL n)
for n,g in n do printfn "%d->%A" n (g|>List.map(fun(_,_,n)->n)|>List.min)
</lang>
{{out}}
<pre>
1->1
2->2
3->4
4->6
5->16
6->12
7->64
8->24
9->36
10->48
11->1024
12->60
13->4096
14->192
15->144
16->120
17->65536
18->180
19->262144
20->240
21->576
22->3072
23->4194304
24->360
25->1296
26->12288
27->900
28->960
29->268435456
30->720
31->1073741824
32->840
33->9216
34->196608
35->5184
36->1260
37->68719476736
38->786432
39->36864
40->1680
41->1099511627776
42->2880
43->4398046511104
44->15360
45->3600
46->12582912
47->70368744177664
48->2520
49->46656
50->6480
51->589824
52->61440
53->4503599627370496
54->6300
55->82944
56->6720
57->2359296
58->805306368
Real: 00:00:01.079, CPU: 00:00:01.080, GC gen0: 47, gen1: 0
</pre>
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